1. Field of the Invention
The present invention pertains to methods and apparatus employing an electromagnetic probe operable for monitoring flow volumes such as the flow volume of an individual phase within a multi-phase mixture that may include a gas as one phase. A particular embodiment of the present invention is especially suitable to life science instrumentation and techniques to provide an electronic flow volume monitor to measure and record urinary output volume for use in a micro-gravity environment, where liquid volume measurements are typically more difficult to make.
2. Description of Prior Art
Generally, the features of the present invention are applicable to usage in percentage flow volume measurements such as for (1) determining the amount of a material in solution such as salt in water, (2) distinguishing and/or monitoring fluid mixtures of fluids having relative permeabilities that are very close such as two alcohols or two oils, (3) determining volume fractions of substantially immiscible fluids such as of oil and water in a flowline, (4) detecting impurities in water, (5) monitoring condensed fluid content within an air stream, and the like.
The present invention is also uniquely suited to the life science problem of measurement of urinary output volume in a micro-gravity environment. Space voyages, especially long term space voyages, in diminished gravity or weightlessness conditions are often detrimental to the health of human space travelers. The relative ease that the heart experiences by pumping blood in a weightless environment produces a cardiovascular de-conditioning effect. Also, without a gravitational force, body fluids tend to migrate upwards in the body to create congested areas.
Therefore, obtaining accurate and consistent measurement of fluid intake and outflow is important for monitoring the health and condition of persons involved in spacecraft missions. Acute changes in urine flow can be the earliest evidence of change in a person's health related to renal blood flow and may occur even before changes in the vital signs of blood pressure, temperature, pulse, or respiration.
The urinary output volume measurement system presently in use on the Space Shuttle utilizes a centrifuge phase separator to allow the taking of volume measurements in a micro-gravity environment. A pressure sensor at the perimeter of the centrifuge phase separator housing measures the force produced when the liquid therein, that is collected and dumped by means of a valve mechanism, is rotated by a drive motor at a constant 400 rpm. The pressure reading from the pressure sensor is related to the volume of the liquid. The centrifuge phase separator requires several minutes to provide a measurement, it adds about 20 kilograms of weight to the flight load, and it absorbs approximately 140 watts of power during operation. Thus, it is desirable to have a substantially non-mechanical measurement device that is lighter, smaller, more accurate and requires less power and time to complete a measurement cycle.
Numerous patents relate to the measurement of medically significant fluids. Urinary output may be measured for many purposes and is related to urinary tract health, blood pressure, heart condition, sodium intake, renal obstruction or failure, and changes in the perfusion of major organs such as the kidney.
U.S. Pat. No. 4,532,936 to LeVeen et at. discloses an apparatus that measures urinary output optically, totalizes the measurement, and prints it on a self-adherent paper which can easily be affixed to a hospital chart. The apparatus includes a measurement column, an optical sensor to determine when the measurement column is empty, a peristaltic pump to empty the measurement column at a known rate, and control logic to determine the volume removed from the column based on the pump rate. A display is also provided for easy observation of current output statistics.
U.S. Pat. No. 4,343,316 to C. A. Jespersen discloses a urine flow monitor for digitally displaying total patient urinary output and flow rate. Urine from the patient passes through a catheter and into a calibrated volume chamber having electronically controlled valves located both above and below the chamber. With the lower valve closed, filling of the chamber takes place until the point where the level reaches an optical sensor at which time the upper valve closes and the lower valve opens to dump the contents. A signal is sent to a console monitor to record the volume dumped and to commence operation.
U.S. Pat. No. 4,891,993 to K. R. Barker discloses an apparatus and method for measurement of urinary output volume. The invention provides a device for establishing a stream of uniform flow from the urinary output. The beginning and ending times of the uniform flow is established by changes in resistivity monitored with electrodes. Because a uniform flow is provided, timing of the duration of the stream provides a measurement of urinary output volume.
U.S. Pat. No. 4,448,207 to J. H. Parrish discloses a urinary output measuring system that includes a gimbal mounted frame that supports a urine container of fixed dimensions to thereby collect urine from a urinary catheter attached to a patient. An ultrasonic transceiver mounted above the container and operated in conjunction with a microprocessor based control unit, periodically measures the height of urine collected in the container. The measured fluid height is used to calculate fluid volume by the control unit. To maintain sterility of the container, the ultrasonic transceiver is mechanically isolated by elements that allow the ultrasonic energy to be transmitted into and received from the interior of the container.
U.S. Pat. No. 5,265,482 to Davis et al. discloses a container that is scanned bottom-to-top and top-to-bottom with a capacitive sensor to detect liquid interfaces therein. The interfaces are coded, their relative heights are stored, and the codes are compared to determine whether the measurements are internally consistent. If the measurements are consistent, then the code and height information is used to sample a desired layer. The system may be used to withdraw a particular layer from a separable fluid such as blood that, after separation, may include red blood cells at a lower position in the container, a separation gel above the red blood cells, plasma above the separation gel and air on the top.
Various patents relate to micro-gravity waste elimination systems including U.S. Pat. No. 3,405,409 to F. M. Bennett, U.S. Pat. No. 3,329,974 to N. Belasco et al., U.S. Pat. No. 3,340,544 to R. T. Cella, and U.S. Pat. No. 5,005,457.
U.S. Pat. No. 5, 176,326 to Blackmon et at. discloses a fluid ejection nozzle which facilitates a wide distribution of fluid therefrom and which permits the fluid flow rate to be easily adjustable. The nozzle is particularly adapted to a heat rejection system useful in a space environment. The nozzle includes a flow distributor positioned within an orifice of the nozzle housing which is comprised of a tongue member and an attached flow control block.
U.S. Pat. No. 5,101,163 to J. Agar discloses a device for measuring the concentration of two substances through the transmission of electromagnetic waves. The device utilizes at least one transmission element for transmitting a signal and at least two receiving elements for receiving signals from the at least one transmission element for measurement purposes.
U.S. Pat. No. 5,099,697 to J. Agar discloses a device for measuring multiphase fluid flow having a flow restrictor, first and second flow meters, and first and second pressure measurement means. No disclosure of electromagnetic wave measurements is made.
U.S. Pat. No. 5,101,367 and U.S. Pat. No. 5,263,363 to J. Agar discloses a method and apparatus for measuring the percentages of oil and water present in an oil/water mixture that requires measurement of energy absorption properties as well as flow data from a flow meter to determine which of various data curves to select so as to obtain an appropriate oil/water mixture reading. The preferred flow meter is a positive displacement flow meter and therefore necessarily mechanical in operation. U.S. Pat. No. 4,503,383 to Agar et al. discloses a device for detecting an interface between two fluids of differing electrical properties using a probe that requires an air core therein.
A paper entitled "Electromagnetic Probe Technique For Fluid Flow Measurements" by J. R. Carl and G. D. Arndt, who are listed as inventors of the present invention, describes an exemplary system that utilizes microwave techniques for measurements made on fluids. However, the system and antenna have other design constraints. For instance, the antenna does not include an orifice through which all fluids preferably flow. As well, the system does not include a separate conductance probe.
A microwave watercut monitor is disclosed in related patents including U.S. Pat. No. 4,947,128 to Hatton et al., U.S. Pat. No. 4,947,129 to Helms et al., and U.S. Pat. No. 4,977,915 to Marrelli. The co-variance microwave watercut monitor requires a test cell suitably constructed to include antenna wave guides and a flow path adapted to receive the flowway of a petroleum stream. A detector assembly connected to the circulator detects the intensity of the test microwave energy. The watercut is indicated in accordance with the intensity signal and the phase difference between the source provided microwave energy and the test microwave energy.
A monitoring system and method for detecting the presence or absence of a material at a location by utilizing an antenna and a control unit is disclosed in related patents including U.S. Pat. No. 4,589,281, U.S. Pat. No. 4,226,118, U.S. Pat. No. 4,169,543; and U.S. Pat. No. 4,222,267 to J. L. Adrich. The antenna provides a signal if material affecting the impedance of the antenna is in the sensing area.
U.S. Pat. No. 3,807,231 and U.S. Pat. No. 3,935,970 to R. L. Spaw disclose automatic level control systems using a single length of insulated, stranded steel cable as a radiating antenna whose reactance varies as a function of the level of material in the container adjacent the antenna.
Several patents are concerned with determining fluid flow rates. U.S. Pat. No. 4,402,230 to A. C. Raptis is directed to measurement of flow velocities of individual phases of multi-phase flow, using two probes located at different positions separated along the flow. Matched filter techniques are employed to identify the spectral signals of the individual phases, and the output signals are cross-correlated to determine the transit delay for each phase between the probes, which may be either optical, thermal or acoustical types. U.S. Pat. No. 4,459,858 to L. B. Marsh discloses an intrusive probe for use in measuring the velocity of a flowing fluid. The probe includes an electromagnet for generating an electromagnetic field in the moving fluid, and a plurality of electrodes for producing electrical signals in response to the flow of fluid through the electromagnetic field.
U.S. Pat. No. 4,554,828 to F. Doll discloses another intrusive probe including a coil for generating a magnetic field through which flows the fluid whose flow rate is to be measured. Electrodes provide a mechanism for obtaining a voltage that is proportional to the fluid flow rate. The probe is immersed in the moving fluid, and flowing fluid passes through a channel through the probe.
U.S. Pat. No. 4,659,218 to de Lasa et al. discloses fiber optic probes for sensing light intensity in monitoring characteristics of bubbles in two and three phase systems.
A level detector is disclosed in U.S. Pat. No. 5,048,335 to Marsh et at. A resonant circuit includes a capacitance probe disposed in a vessel so as to be responsive to variations in capacitance as a function of the level of material in the vessel. An oscillator is coupled to the resonant circuit and to a phase detector for detecting variations in phase angle as a function of the capacitance of the probe. The output of the phase detector is used to obtain an indication of the level of material.
U.S. Pat. No. 5,140,270 to Martin et at. discloses an apparatus for determining the quality of the dielectric material in a transformer bushing. The device uses the bushing as a capacitive element to determine the interior condition of the bushing.
Consequently, there remains a need for lightweight, accurate, low power instrumentation and techniques to make flow volume measurements of an individual phase in a multi-phase flow. Those skilled in the art have long sought and will appreciate that the present invention provides solutions to these and other problems.